4.3 Proteins

CHAPTER 4 : CHEMICAL COMPOSITION OF THE CELL

PREPARED BY : MUHD FAZLI B. DOLLAH SBPI GOPENG

• Elements : C, H, O, S, N & P. • Large & complex molecules • Monomer : amino acid • Molecules of amino acids are joined together through condensation • Amino acids are joined together by peptide bond • Amino acid + amino acid  dipeptide + water – Polypeptides are formed when many molecules of amino acids are joined together to form long chains of a.a. • Polypeptides broken down through a series of hydrolysis reactions to become dipeptides & finally amino acids.

• 20 amino acids found in the proteins of living cells • Two types of a.a. : • Essential amino acids : cannot synthesised by body cells • Non-essential amino acids : can be synthesised by body cells

• Food that contain all the essential a.a. are called 1st class protein. (milk, meat, eggs) • Food that lacks a few essential a.a. are 2nd class protein. (corn)

Protein Structures • Primary structure : a long straight chain of polypeptide • Secondary structure : coiled to form helix or pleated sheet. • Tertiary structure : helix or pleated sheet is folded in various ways to form globular protein • Quarternary structure : folded protein chains are joined together to form a single protein